question about co2 ???

as long as you have good ventilation, added co2 is not nessecary. but if your grow room is sealed air tight then i'd use some form of co2 supplementation. do a search on "yeast" and you'll see a recipe for a co2 "generator" that uses yeast, sugar, water and a soda bottle. in essence you combine 2 cups sugar, 2 to 4 cups hot water (not boiling as yeast will die if subject to temps above 130f) and a tablespoon or so of yeast (not rapid rise) and mix. poke a small hole in the lid of bottle cap so the co2 can escape. the yeast eats the sugar and the byproduct is co2! put the bottle in front or behind your fan, or above the plants as co2 is heavier that air and will go right over the plants. but like i said search for the recipe as i might have missed a detail or two.